The human race, indigenous and non-indigenous alike, is about to cross a threshold, though it is not one of evolution and is nothing to brag about, scientists say.

For the first time in human history, concentrations of carbon dioxide in the atmosphere is on the verge of hitting 400 parts per million, according to the federal National Oceanic and Atmospheric Administration (NOAA).

“Crossing 400 ppm is not a reason for celebration,” said Pieter Tans, a scientist with NOAA’s Global Monitoring Division, after the latest reading was released from the Mauna Loa Observatory in Hawaii. “Once emitted, the added CO2 does not disappear from the atmosphere and oceans for thousands of years, making it progressively more and more difficult to avoid a degree of climate change that would likely force painful adaptation.”

Carbon dioxide is the primary greenhouse gas contributing to climate change, and it is common knowledge that the amount has been increasing at an alarming rate for decades. The primary human activity affecting the amount and rate of climate change is greenhouse gas emissions from the burning of fossil fuels, which releases large amounts of carbon. This of course increases CO2 concentrations in the atmosphere, increasing the greenhouse effect and causing Earth’s surface temperature to rise, according to the U.S. Environmental Protection Agency's official explanation. This latest reading, taken by the NOAA Earth System Research Laboratory Global Monitoring Division, showed carbon dioxide levels at 399.54 parts per million as of May 5.

Charles David Keeling was the first to document the rise in carbon dioxide concentration. Keeling laid the basis for investigating the global behavior of atmospheric CO2, known as the Keeling Curve, using infrared gas analyzers to measure the atmospheric CO2 concentration at remote locations around the world. He recorded an atmospheric CO2 concentration of 313 parts per million at Mauna Loa in March 1958.

Analysis of bubbles in ice cores at different depths in ice sheets prior to 1958 shows that CO2 atmospheric levels have risen steadily from 280 parts per million at the start of the industrial revolution two centuries ago, according to two researchers at the University of Wyoming.

“This is one milestone no one should be happy about reaching,” said Citizens Climate Lobby executive director Mark Reynolds in a statement. “Our civilization has altered the balance that nature carefully maintained for hundreds of thousands of years. We risk tragic consequences if we fail to restore that balance.”

The CCL lobby advocates passage of a steadily-increasing, revenue-neutral carbon tax that returns proceeds to Americans, a proposal they say is supported by a number of conservatives, including former U.S. Secretary of State George Shultz, as a way to employ the power of the free market to shift away from the use of fossil fuels. CCL also recommends coupling the carbon tax with border adjustment tariffs on imports from nations that lack equivalent carbon pricing, which they say would provide the incentive for other nations to adopt their own carbon taxation. The rise has contributed to a sense of urgency at deadlocked United Nations Framework Convention on Climate Change (UNFCCC) talks in Bonn. 

“We are just about to cross the 400 parts per million threshold, hence this conference meets in a heightened sense of urgency,” said framework convention executive secretary Christiana Figueres in opening the latest session, which ran from April 29 through May 3. “We must meet the deadlines set by the UNFCC’s Conference of the Parties. The ADP working group has already used one third of the time allocated, so we must use the remaining time wisely.”